For purposes of the study, “ad hoc risk communication” was defined as information that correctly advises members of the public about the safety of childhood vaccines but that misrepresents the extent, nature, and consequences of public concern over vaccine risks.

The refrain that “low vaccination rates” are fueling a “resurgence” in childhood disease also is not factually supported. Eliminated in the United States, measles outbreaks can still occur when individuals contract the disease abroad. Fortunately, “[h]igh MMR vaccine coverage in the United States (91% among children aged 19–35 months),” the CDC states, “limits the size of [such] outbreaks.” “[D]uring 2001–2012, the median annual number of measles cases reported in the United States was 60 (range: 37–220).”

The incidence of pertussis, or “whooping cough,” has increased dramatically in recent years. But “[p]arents refusing to get their children vaccinated,” according to the CDC, are “not the driving force behind the large scale outbreaks” of this disease. In addition to “increased awareness, improved diagnostic tests, better reporting, [and] more circulation of the bacteria,” the CDC has identified “waning immunity “from an ineffective booster shot as one of the principal causes” (ibid). Experets outside the CDC concur (Cherry 2012).

There are enclaves, the CDC cautions, in which vaccination rates are significantly lower than the national average, and in which the extent and duration of pertussis and mealses outbreaks are likely to be enlarged.

These enclaves thus pose a genuine public health concern. They merit study aimed at understanding the influences that generate them and at formulating risk-communication strategies that might be employed to counteract and contain them.

What the Study was directly designed to assess was the impact of empirically uninformed, ad hoc risk communication on public beliefs about vaccine safety. Its findings suggest that the exaggerations and miststatements of fact that dominate such communication themselves pose a threat to public support for universal immunization programs.

The herd immunity conferred by universal vaccination is a collective good. Individuals tend to contribute to public goods, research suggests, when they believe others are voluntarily doing so but refrain from contributing when they think others are shirking or free-riding (Gintis et al. 2004).

This dynamic—which has been found to explain varying levels of tax compliance, charitable giving, voting, and other forms of behavior (Kahan 2004)—has been shown to influence the intention of people to get vaccinated as well (Hershey et al. 1994).

In the CCP study, it was found that exposure to typical forms of ad hoc risk communication tend to induce individuals to substantially overestimate the percentage of parents who refuse to vaccinate their children and to underestimate vaccination rates.

This is a troubling result, for it implies that exposure to the exaggerations that pervade ad hoc risk communications could in fact weaken popular motivations to contribute to the collective good of herd immunity.

Another theme of ad hoc risk communication attributes the asserted decline in vaccination rates to an “anti-science” sensibility linked to disbelief in evolution and climate-change skepticism.

The survey component of the study found that attitudes about vaccine are not meaningfully related to either belief in evolution or positions on climate change: individuals on both sides of both issues overwhelmingly perceive vaccine benefits to be high and vaccine risks to be low.

In the experimental component of the study, however, subjects exposed to a communication patterned on ones using the anti-science trope did show signs of polarizing along lines that reflect cultural contestation over other risks, including climate change, legalizing marijuana, and instructing high school students on birth control.

This finding too is disturbing. The entanglement of positions on risks and like facts interferes with the capacity of ordinary citizens to recognize valid science and interferes with constructive public deliberations (Kahan, Peters, Dawson & Slovic 2013). It was exactly this dynamic that generated political controversy and persistent public ambivalence over the HPV vaccine.

The premise of ad hoc risk communication—that there is growing resistance and controversy over the safety of childhood vaccines—is false.

Propogating this claim, however, creates the risk of exactly such resistance and conflict.

Research of the Cultural Cognition Project is or has been supported by the National Science Foundation; by the Annenberg Public Policy Center at the University of Pennsylvania; by the Skoll Global Threats Fund; by the Putnam Foundation; by the Woodrow Wilson International Center of Scholars; by the Arcus Foundation; by the Ruebhausen Fund at Yale Law School; by the Edmond J. Safra Center for Ethics at Harvard University; and by GWU, Temple, and NYU Law Schools. You can contact us here.